1. Field of the Invention
The present invention relates to injection molding machines, and, more particularly, to the die closing unit of an injection molding machine and to a slide support and adjustable guide shoes for the movable die carrier plate of such a die closing unit.
2. Description of the Prior Art
The prior art in the field of injection molding machines encompasses at least three basic machine types which differ in the arrangement of their die closing units, and particularly with respect to the arrangement of the hydraulic drive for the movable die carrier member. The so-called pull-type die closing unit normally features two or four drive cylinders in a parallel arrangement, with piston rods which reach past or through the injection molding die, having their distal extremities attached to the movable die carrier plate. The weight of the latter may be carried by the piston rods alone, but, preferably, it is supported on a cantilever-type guide frame by means of rollers or sliding guide shoes. Such a die closing unit is disclosed, for example, in U.S. Pat. No. 3,674,400 and in U.S. Pat. No. 3,841,823.
In a push-type die closing unit, a movable die carrier plate, or a die carrier frame, is longitudinally guided on two or four stationary tie rods which extend between two stationary plates on the machine base, thus forming a rigid guide frame with the latter. The movable die carrier member is pushed into its closed position, either by means of a transversely oriented hydraulic actuator which drives a knee linkage, or by means of an axially aligned hydraulic actuator whose piston rod extends parallel to the tie rods in the center axis of the die closing unit. This third type of die closing unit is much more compact than the knee-linkage-type die closing unit, and it is therefore frequently preferred over the latter, especially in the case of heavy-duty injection molding machines. Such a die closing unit is shown, for example, in U.S. Pat. No. 4,094,621.
Most in-line push-type die closing units for heavy-duty applications utilize four tie rods which are arranged at the four corners of a square, with their extremities rigidly clamped to the stationary die carrier plate and to the head plate of the power cylinder, respectively. While such an arrangement ordinarily offers excellent guide conditions and alignment accuracy for the movable die carrier frame riding on the four tie rods, it has been found that, over extended periods of service, the guide bushings of the die carrier frame suffer wear to the extent that the alignment accuracy of the injection molding die halves deteriorate, and, consequently, the dimensional consistency of the injection-molded parts decreases. The replacement and fitting of new guide bushings in the die carrier frame is time consuming and, costly, because, in most cases, it must be done by the manufacturer.
It has therefore already been suggested to use exterior guide elements to support the movable die carrier member, in an attempt to at least partially relieve the tie rods, or the piston rods, respectively, of their load-carrying function. Frequently, however, such an auxiliary load-carrying guide brings with it operational problems resulting from misalignment and/or the impossibility of precisely measuring and adjusting its load-carrying action.
An adjustable die carrier guide arrangement is disclosed in the above-mentioned U.S. Pat. No. 3,674,400. There, it is suggested that the guide members for a pull-type die closing unit be in the form of sliding guide shoes or guide rollers, with vertical adjustability provided in the form of a threaded spindle, or an inclined plane in conjunction with a spindle, or an eccentric adjustment for guide rollers, or, lastly, a vertically guided spring-loaded slide shoe. To the extent that adjustability is taught in the disclosure of this patent, such adjustability is controllable only with difficulty, if at all, so that the earlier-mentioned wear conditions on the guide bushings will to a large extent, still be present.